Electrical protection of cathoderay tube screens



Patented July 12, 1949 UNITED STATES I ELECTRICAL PROTECTION OF CATHODE- RAY TUBE SCREENS Karl R. Wendt, Hightstown, N. J., assignor to Radio Corporation of America, a corporation of Delaware 10 Claims.

This invention relates to electrical circuit protection and more particularly to the protection of cathode ray tube screens.

It is quite well appreciated in the television art that the electron beam of a cathode ray tube normally has enough energy to cause damage to the tube screen if it is allowed to remain at rest on the tube screen if, for example, the beam deflection system fails.

Electrical circuits for protecting kinescope screens from burning by failure of deflection have long been used. However, they have not been electrically fast enough to protect the screen in all cases.

According to this invention, there is disclosed a novel circuit arrangement which is exceptionally fast and which relies for its power upon stored charges, thus insuring positive extinction of the beam regardless of the condition of any of the normal power supplies.

A primary object of the invention is to provide a means for protecting kinescope screens from burns resulting from loss of deflection due to accident, deflection power loss or normal shutdown in cases where the second anode voltage may decay more slowly than the deflection, and to provide circuits especially adapted to protect three tubes as used in simultaneous color receivers.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which:

Figure 1 illustrates by circuit and block diagram one form of this invention; and

Figure 2 shows by circuit diagram another form of this invention.

In Figure 1, there is shown a cathode ray tube or image producing device I equipped with a cathode ray gun structure including a cathode 3 for developing a beam of electrons. A horizontal or line deflecting coil 5 and a vertical or field deflecting coil 7 are provided in the conventional manner. tion signal energy by a deflection signal generator of the usual type employing a horizontal output tube 9. Although not shown in detail here, the deflection and control circuits may be of the type shown and described in a U. S. patent to Tolson et al., No. 2,101,520, granted December 17, 1937, or in the U. S. patent to Vance, No. 2,137,039, granted November 15, 1938.

Synchronization may be maintained in accordance with any of the well known procedures.

Coils 5 and 1 are provided with deflec- 2 Circuit arrangements for producing images by controlling the intensity of the electron beam 1n accordance with a video signal are well shown and described in the art. For example, signals obtained from a television receiver arranged generally in the manner shown and described in the U. S. reissue patent to Carlson, No. Re. 20,700, granted April 19, 1938, may be employed. It is not intended, however, that the practice of this invention should be limited to its employment therewith.

The generation of the cathode ray beam requires that a relatively high potential be applied to second anode II. This high voltage is supplied by power supply !3 which obtains its energy from a source of commercial power through contacts of relay Hi.

In addition to supplying deflection energy for deflection coils 5 and l, the deflection signal generator also supplies operating current to winding ll of a polarized relay [9 through a resistance element 2! and the diode damper tube 23. A condenser 25 is included in the circuit. It will be seen that if deflection coil 5 does not receive energy, winding ll will not be energized.

Another winding 2? of relay l9 obtains its energizing current from a 3+ source. The 13-]- source may, for example, be an auxiliary source or be that employed in the-associated circuit.

Winding 27 of relay I9 is connected to the 13+ source through and between two resistors 29 and 3|. There is also connected in the circuit of winding 27 a condenser 33 which is connected across the series circuit of resistor 29 and winding 27. Condenser 35 is connected across the series circuit including winding 2'! and resistor 3|.

As applied to the horizontal deflection, for example, this invention consists of a circuit which utilizes the balanced or polarized relay l9, such as a micro-positioner, wherein the one coil 21 is connected to the B+ supply in the direction to maintain the relay open, as indicated by the arrow. The coil ll receives current from a source which is present only when the horizontal deflection circuit is operating, such as, for example, the power feedback voltage, or the damper tube rectified voltage. The coil H is connected so as to maintain the relay closed, as indicated by the arrow, the current being set to such a value that the eflect of the coil 21 is completely overcome during proper operation of the circuit and the relay under normal conditions is closed. Should the current obtained from the deflection system be reduced beyond a critical value due to inade quate deflection, the coil 21 will open the relay.

In the case of the power feedback circuit, the current through the coil I! will actually reverse with low or no deflection, thus further insuring that the relay will open. In the case of 13+ failure, such operation is neither positive nor fast enough. Therefore, in addition to the resistors mentioned in series with the first coil, two capaci-r tors 33 and 35 are provided, connected as shown in Figure 1.

The voltage drop across coil 21 due to current flow through resistances 2d and 31 will be as shown. It will be seen that any drop in the value of B+ will be transmitted to the negative end of coil 27 through condenser 33, and the negative end of the coil 21 will be driven further negative. The positive end of the coil 21, however, will be maintained at its former value lay-capacitor 35.

Thus a decrease in B+ will cause an increase in current through coil 21, the power being supplied by the charge stored in condensers 33 and 35. The relay lfl'is therefore quickly opened, and maintained open long enough for other circuits to disconnect the second anode ll and allow its voltage to fall to a safe value.

This invention also includes novel ways of utilizing such a fast operating relay. In the past, the relay-has been used to open the kinescope cathode circuit. An improvement over such a circuit is shown in Figure 1, in which the kinescope'cathodeais grounded bythe relay l9 during normal operation. The kinescope cathode 3 is also connected through relay E6 to 3+. When the relay I9 contacts are closed, the kinescope cathode '3 is not only grounded, but relay I6 is also operated. Relay-l6 may be used to operate the second anode power supply, as shown. When relay l 9 opens, relay I6 also opens, and the kinescepe cathode 3 rises to 13+ potential through its connection through relay 16, thus extinguishing the kinescope beam.

When three kinescopes are operated together, as in the simultaneous color system, the cathodes may be tied together and operated as described for Figure 1. However, it is usually convenient to apply biasto the separate kinescopes by varying their cathode potentials. This is show-n in Figure 2.

In order to avoid the use of three pairs of relay contacts, it is necessary to include the relay in the common ground circuit, as-shown in Figure 2.

In order to avoid a condition where there will be little or no bias on the kinescope, when the charge on condensers 4t, 43 and 45 has disappeared, a high impedance divider supplies the screen voltage for the three tubes as-shcwn, Thescreen bypass condenser 41 is connected to lead 49, which is connected to the armor relay l9 through a set of contacts. When relay ls 'opens, lead 49 goes to approximately 13+ by virtue of the connection through winding [5 of relay l6 and the cathodes are elevated above B+ by the stored charges on condensers ll, 43 and 45. Condenser 41 also has astored charge, which, during the transient after relay 1!! opens, elevates the screen voltage above 3+. This is immaterial since condensers 4|, 43 and 45 thoroughly cut off the kinescopes. After equilibrium is reached, lead 49 is at B+ and the screen potential returns to its normal value. When normal deflection is restored and relay l9 closes, the kinescope cathodes will go to ground potential, due to the lack of charge on condensers H, 43 and 45-, and the kinescopes will be at or near zero bias. The charge on condenser 41, however, will drive the screen voltage negative, thus cutting off the kinescopes until normal bias returns. Contacts of relay 2'! may be used to remove the main discharge path for condensers 4|, 43 and 45, thus lengthening the time that these capacitors bias the kinescopes ofi, without making them of unduly large capacity.

It will thus be seen that by practicing this invention, a dependable and fast acting protection for the cathode ray tube screens will be provided.

Having thus described the invention, what is claimed is:

, 1. A cathode ray tube screen protective arrangement for a system employing high voltage energy and deflection energy for control of a cathode ray, a source of B+ potential, said cathode ray tube screen having a cathode associated therewith, said cathode ray tube screen protective arrangement comprising in combination a first and a second relay, each having switching contacts, the first of said relays being of the polarized type having a pair of energizing windings polarized to neutralize the eflect of each other upon the application of current to both of the said pair of windings, thesecond of said relays having an energizing winding, the energizing winding ofsaid second relay connected between said cathode and said source of 3+ potential, the switchingcontacts of said second relay being connected to interrupt said high voltage energy upon a sizeable reduction in said B+ potential, one of the windings of said first relay being connected to receive a portion of said deflection energy, the other ofthe windings of said first relay being connected to said source of 3+ potential, and said cathode connected to a reference potential through the switching contacts of said first relay.

2. A cathode ray tube screen protective arrangement for a television system employing high voltage energy and deflection energy for control of a cathode ray of a cathode ray tube and wherein said cathode ray tube has a cathode, said cathode ray tube screen protective arrangement comprising in combination a first and a second relay, each having switching contacts, the first of said relays being of the polarized type having a pair of energizing windings to neutralize the effect of each other upon the application of current to both of the said pair of windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected between said cathode and said source of 3+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a sizeable reduction in said B+ potential, one of the windings of said first relay being connected to receive a direct current portion of said deflection energy, the other of the windings. of said first relay being connected to said source of 3+ potential through a resistor, and said cathode connected to a reference potential through the switchingcontacts of said first relay.

3., A cathode ray tube, screen protective are rangement for a television system employing a high voltage. energy and deflection energy for control of" a cathode ray of a cathode ray tube and wherein said cathode ray tube has a cathode, said cathode ray tube screen protective arrange.- ment comprisin n combination. a first and a se re .v a hav w tching contacts normally closed, during proper operation of the system, the first of said relays being of the polarized type having a pair of energizing windings to neutralize the effect of each other upon the application of current to both of the said pair of windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected between said cathode and said source of 3+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a, sizeable reduction in said 3-}- potential, one of the windings of said first relay being connected to receive a portion of said defiection energy through an electrical rectifier, the other of the windings of said first relay being connected to said source of B+ potential through a. resistor, and said cathode connected to a reference potential through the switching contacts of said first relay.

4. A cathode ray tube screen protective arrangement of the type suitable for a television system employing high voltage energy and deflection energy for control of a cathode ray of a cathode ray tube and wherein said cathode ray tube has a cathode, said cathode ray tube screen protective arrangement comprising in combination a first and a second relay, each having switching contacts normally closed during proper operation of the system, the first of said relays being of the polarized type having a pair of energizing windings wound to neutralize the effect of each other upon the application of current to both of the said pair of windings, the second of said relays having an energizin winding, the energizing winding of said second relay connected between said cathode and said source of 3+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a failure of said 3-}- potential, one of the windings of said first relay being connected to receive a portion of said deflection energy, the other of the windings of said first relay being connected to said source of 3+ potential through and between a pair of resistance elements, a first capacity connected across the series circuit involving one of said resistance elements and said other winding, and a second capacity connected across the series circuit involving the other of said resistance elements and said other winding, and said cathode connected to a reference potential through the switching contacts of said first relay.

5. A cathode ray tube screen protective arrangement for a television system employing high voltage energy and deflection energy for control of a cathode ray tube cathode ray and wherein said cathode ray tube has a cathode, said cathode ray tube screen protective arrangement comprising in combination a first and a second relay, each having switching contacts normally closed during proper operation of the system, the first of said relays being of the polarized type having a first and a second energizing winding which are wound to neutralize the efiect of each other upon the application of current to both of the said windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected between said cathode and said source of B+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a reduction in said B+ potential, the first of the windings of said first relay connected to receive a portion of said deflection energy, the second of the windings of said first relay being connected to said source of 3+ potential through and between a pair of resistanc elements, a first capacity connected across the series circuit involving one of said resistance elements and said second winding, and a second capacity connected across the series circuit involving the other of said resistance elements and said second winding, and said cathode connected to a reference potential through the switching contacts of said first relay.

6. A cathode ray tube screen protective arrangement for a color television system employing high voltage energy and deflection energy for control of a cathode ray, a source of 13+ potential, and having a plurality of cathode ray tubes, each having a cathode, said cathode ray tube screen protective arrangement comprising in combination a first and a second relay, each having switching contacts, the first of said relays being of the polarized type having a first and a second energizing winding polarized to neutralize the eifect of each other upon the application of current to both of the said windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected between said cathodes and said source of 3+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a sizeable reduction in said B+ potential, the first winding of said first relay being connected to receive a portion of said deflection energy, the second winding of said first relay being connected to said source of 3+ potential through and between a pair of resistance elements, a first capacity connected across the series circuit involving one of said resistance elements and said second winding, and a second capacity connected across the series circuit involving the other of said resistance elements and said second winding, and said cathode connected to a reference potential through the switching contacts of said first relay.

7. A cathode ray tube image screen protective arrangement for a television system employing high voltage energy and deflection energy for control of a cathode ray, a source of 13+ potential, said cathode ray tube having a cathode, said cathode ray tube image screen protective arrangement comprising in combination a first and a second relay, each having switching contacts, the first of said relays being of the type having a pair of energizing windings polarized to neutralize the efiect of each other upon the application of current to both of th said pair of windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected serially with switching contacts of said first relay, and said sourc of 3+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a sizeable reduction in said B+ potential, a damper tube connected to receive a portion of said deflection energy, one of the windings of said first relay connected to said damper tube to receive a rectified portion of said deflection energy, the other of the windings of said first relay being connected to said source of 3+ potential through and between a pair of resistance elements, a first capacity connected across the series circuit involving one of said resistance elements and said other winding, and a second capacity connected across the series circuit involving the other of said resistance elements and said other windings, and said cathode connected to a reference potential through the switching contacts of said first relay.

8. A cathode ray tube image screen protective arrangement for a television system employing high voltage energy and deflection energy for control of a cathode ray, a source of B+ potential, said cathode ray tube-screen having a'cathode, said cathode ray tube image screen protective arrangement comprising in combination a first and a second relay, each having switching contacts, the first of said relays being of the type having a pair of energizing windings polarized to neutralize the effect. of each other upon the application of current to. both of thesaid pair of windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected serially with switching contacts of said first relay, and said source of 3+ potential through a resistor, the switching contacts of said second relay being connected to interrupt said high voltage energy upon a sizeable reduction in said B+ potential, a damper tube connected to receive .a portion; of said deflection energy, a resistor, a condenser and an electrical load for said source of B+ potential, a series circuit including one of the windings of said first relay and said resistor, said seriescircuit connected between said source of 3+ potential and said electrical load, said condenser connected in parallel with said series circuit, the

other of the windings of'said first relay being con- 9 A cathode ray tube image screenprotective arrangement for a television system employing high voltage energy and deflection energyior control of a cathode ray, a source of 13+ potential, said; cathode ray tube screen having a cathode and a, screen electrode, said cathode ray tube image screen protective arrangement comprising in combination a first and a second relay, each having switching contacts, the first of said relays being of the type having a pair of energizing windings polarized to neutralize the effect oi each other upon the applicationof current to, both of. the said pair of windings, the second of said relays, having an energizing winding, the energizing Winding of said second relay connect.- ed serially with switching contacts. of said first relay and said source of 3+ potential, a condenser, said condenser connected, between said screen electrode and the point of connection be- :tween said energizing Winding of said second relay and switching contacts of said first relay, the switching'contacts of said second relay being connected to interrupt said high voltage energy upon asizeable reduction in said B+ potential, one of the windings of said first relay being connected to receive a portion of said deflection energy, the other .of the windings of said first relay being connected to. said source of 3+ potential, and said cathode connected to a reference potential through the switching contacts of said first relay.

10:. Acat'node ray tube image screen protective arrangement. for a television system employing high voltage energy and deflection energy for con- :trol of a. cathode ray, a source of 18+ potential, said cathode ray tube screen having a cathode and a screen electrode, said cathode ray tube image screen protective arrangement comprising in combination .a first and a second relay, each having-switching contacts, the first. of said relays being of the type having a pair of energizing windings polarized to neutralize the eflectof each other upon the application of current to both of the said pair of windings, the second of said relays having an energizing winding, the energizing winding of said second relay connected serially with switching contacts of said first relay and said source of B+ potential, a condenser, said condenser connected between said screen electrade and the point of connection between said energizing winding of said second relay and switching contacts of said first relay, the switching contacts of said second relay being connected to-interruptsaid high voltage energy upon a sizeable reduction in said B+ potential, one of the windings of said. first relay being connected to receive. a. portion of said deflectionenergy, the other of the windings. of said first relay being connected to said source of 13+ potential, said cathode connected to a reference potential through theswitching contacts of said first relay, and saidscreen electrode connected to said source'ot 3-]- potential through a resistive voltage divider.

KARL R. VIENDT.

No: references cited. 

